YJ needs a bigger brake master cylinder

jeepeater2003

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Joined
Mar 21, 2005
Location
raleigh
I have chevy 3/4 ton front and 1 ton rear axles. 4 wheel disc. Chevy big piston calipers in the front and regular calipers in the rear. My stock master cylinder doesnt seem to put out enough fluid to make the big pistons really grab. Is there a directy bolt in anyone knows of that will fit with my original brake booster or am i going to have to change the whole setup, brake master and brake booster?
 
i was under the impression that a chevy... 86 maybe? k20 would bolt on.....

there IS a bolt on... and i'm almost positive it is a chevy... though i'm unsure what model specifically....

that was actually on my list of things to research tonight... i'll post what i find when i find it.

-Erik <--- running the massive ford dual piston caliers up front and chevy front calipers in the rear... same problem
 
80's model E350 van MC...you have to drill out the holes to fit, but its not hard at all. I want to say part #M1008 at AutoZone, don't quote me on that though. I'm running one and it works great! I'm on 60s and 38s, no problems.
 
Yeah you will need to drill the holes to 9/16 then grind down the egdes so it will fit in.
 
BigWheelBob said:
I think you want the Mercury Marquis master cyl. for rear disk setups.
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I am using the merq mc on my cj, (it had a yj mc and booster) and it works awesome. it should be a direct bolt on to your yj. Just get one for a 78 with 4wh disks and hydroboost. :beer:
 
Alright so i use the stock brake booster and the master cylinder form either a 78 mercury marquis, or stock brake booster and a master cylinder from a 80s model E350 and have to do some mods? I am just making sure i am reusing my original brake booster, first off because it is brand new and second, i dont want to spend any extra money if it is not needed.
 
yeah the E350 should work just fine. I used mine on a 9" and front chevy calipers. PM me if you need any help with it.
 
does anyone think that going from the stock 35 to a scout rear dana 44 would be too much for the stock master cylinder in the mj?

it seems like we bled it a thousand times, but finally got it to have nice firm brakes , then a month later swapped in the 44 and haven't had brakes since

im guessing that the booster/MC setup is the same or very close to the vehicles mentioned here, and i would like to upgrade it if it seems neccessary, i just have a hard time believing that the d44 wheel cylinders are THAT much bigger, but i am also running the newer style calipers on the front 30, off of a '99, maybe these need more fluid volume, also contributing to the problem?
 
one thing you can do if you dont want to swap MC, is adjust the "push" on the MC. I'm not sure if this will only mask the problem but heres what you do. Pull the MC off the booster. You will see a "pin" coming out of the center of the booster. Pull the "pin" out of the booster and un-screw it. Reinstall. You want to do this a little at a time, if you go to far then your brakes will be applied all the time. You will notice if you have done this after a few miles b/c your brakes will heat up and feel like a sticky caliper.
 
awspence said:
does anyone think that going from the stock 35 to a scout rear dana 44 would be too much for the stock master cylinder in the mj?

it seems like we bled it a thousand times, but finally got it to have nice firm brakes , then a month later swapped in the 44 and haven't had brakes since

im guessing that the booster/MC setup is the same or very close to the vehicles mentioned here, and i would like to upgrade it if it seems neccessary, i just have a hard time believing that the d44 wheel cylinders are THAT much bigger, but i am also running the newer style calipers on the front 30, off of a '99, maybe these need more fluid volume, also contributing to the problem?
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It should work fine ther must be somthing else wrong.
 
hmmm, thats what i was afraid of, but kinda what i had always figured, i went through the brakes, besides the lines, booster, and prop valve there isnt anything that hasnt been replaced

the PO installed and said he bench bled the master cylinder, and since i had it working with the 35, i feel like the MC should be fine, i havent touched it since the first time i got it working...... i guess im overlooking something , but i sure cannot figure it out
 
jeepeater2003 said:
Alright so i use the stock brake booster and the master cylinder form either a 78 mercury marquis, or stock brake booster and a master cylinder from a 80s model E350 and have to do some mods? I am just making sure i am reusing my original brake booster, first off because it is brand new and second, i dont want to spend any extra money if it is not needed.
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Remember, as stated in my tech write up and the one on pirate, the E350 swap is good ONLY for front disc/rear drum setups. The others, Merc, Vette are for disc/disc setups. You CAN use the stock Jeep booster with the E350 swap, works fine.
 
Alright so who knows what exactly i would have to do with the master cylinder from the 78 mercury marquis. Will it bold directly in with the use of my original brake booster or what. I am running 4 wheel disc. Any help would be appreciated.
 
yes it will bolt right up
 
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